1. Field of the Invention
The present invention relates to an imaging device, in which an image formed by an image-forming optical system is bent by prism to be incident on an imaging sensor.
2. Description of the Related Art
When pursuing further downsizing/miniaturization of imaging devices, incorporated in mobile electronic devices such as mobile phones, a further reduction in the diameter of each optical element is required. However, a smaller diameter optical element causes insufficient light quantity in the peripheral (marginal) area of imaging surface. Since the imaging surface has a rectangular shape (i.e., not a square shape), the peripheral light quantity along the long sides (the peripheral light quantity in the direction parallel to the long sides of imaging surface, i.e., the portions in the vicinity of the short sides of imaging surface) is considerably smaller than the peripheral light quantity along the short sides (the peripheral light quantity in the direction parallel to the short sides of imaging surface, i.e., the portions in the vicinity of the long sides of imaging surface). In particular, there are some imaging devices in which a prism (bending optical system) is provided at the front of an imaging sensor in order to satisfy demands for slimming down the size of the body in which the imaging device is installed. In such a structure, the imaging device would face a problem of being unable to enlarge the lens diameter at the front of the prism, which worsens the peripheral light quantity along the long sides of the imaging surface. Therefore, in order to reduce the difference between peripheral light quantity at the short sides and the peripheral light quantity at the long sides of a rectangular shaped imaging sensor, much effort has been made to increase the peripheral light quantity along the long sides, in other words, to increase the light quantity at the whole peripheral portions (regardless of short sides and long sides).
An example of the related art is disclosed in Japanese Unexamined Patent Application No. 2008-242446.
The present invention provides an imaging device configured of an imaging sensor having a rectangular imaging surface, an image-forming optical system for forming an image on the imaging surface, and a prism positioned between the image-forming optical system and the imaging sensor to bend the optical path, in which the peripheral light quantity difference between the short sides and the long sides on the rectangular imaging surface is reduced.